Ever since human beings subjected themselves to excessive noise, they have sought to protect themselves from the noise and to deaden or dull the transmission of the noise to the ear drum and human senses. All variety of devices have been stuffed in and hung over humans' ears to achieve the desired result--wads of cotton, fibrous plugs, stretchable envelopes with deformable fillers, acoustic barrier discs, thin walled resilient air filled chambers adapted to be forced into the ear canal, and various ear muffs and covers.
Ear muffs or covers designed to achieve the desired result must essentially be clamped to the head over the ears, usually by means of a bowed leaf spring connected to both covers and extending over the top of the user's head. Such covers tend to be very bulky and uncomfortable, causing the user physical irritation and distress. Consequently, considerable effort has been expended to develop ear plugs that can be inserted in the ear, either within the ear canal and/or within the folds of the outer ear to be comfortably supported by the ear itself without extraneous springs or other fastening devices.
Acoustic ear plugs tend to be very small in order to fit within the ear canal and/or outer ear and to be of sufficiently light weight as to be comfortably supported by the ear itself. Wads of cotton and other fibrous materials easily adapt to the structure of the ear and are light weight, but they provide relatively small acoustic barrier values Thin walled resilient air filled chambers, such as shown in U.S. Pat. Nos. 3,259,128 to Leight and 4,089,332 to Rose, can easily be inserted in the ear canal and, due to their resiliency and internal pressure, will expand into and completely fill the recesses of the canal. Such devices have been reasonably successful and claim a noise reduction rating of 26 decibels.
Another approach to the subject, as disclosed in U.S. Pat. No. Re. 29,487 to Gardner, involves the use of an elongate cylindrical plug comprised of certain polymeric foam materials having sound barrier properties and also having compression recovery characteristics such that following compression for insertion into the ear canal the plug can slowly recover and expand into conformity with the interior structure of the canal and thereby establish substantially complete obturation.
While these proposals have provided certain advances in the art, it remains that ear plugs having even greater acoustic barrier capabilities are desired. For purposes of greater obturation of noise, it would seem that vacuum would be an ideal medium. However, based on the prior publications presently known, it would appear that evacuated chambers have not achieved acceptance in the acoustic ear plug art.
German Pat. No. 225,607, granted in 1910, discloses the use of an evacuated chamber in the formation of an acoustic ear plug. In two of the three illustrated embodiments (FIGS. 1 and 2), a spherical vacuum chamber is formed from a hard material and covered with an elastic material, which in the case of FIG. 2 is relatively thick and further provided with a cover. In the FIG. 3 embodiment, a spherical vacuum chamber is filled with cotton "to support the cover over the vacuum". The specification, which is very abbreviated, states that the sphere can be replaced with any anatomic shape, but contains no specifics. Presumably, this disclosure has not found acceptance in the art due to the need for a rigid or incollapsible vacuum chamber structure and a consequent inability to adapt such structure to the variable conformations of the human ear to seal off or substantially completely obturate the ear canal. The spherical chamber of the German patent appears most difficult to work with and the least susceptible to provision of both a vacuum chamber of effective size and at the same time sufficient spacial tolerance to accommodate an adequate body of elastic material capable of obturating the canal.